Growth of a freely-propagating, two-dimensional turbulent-like flame

Using a thin flame model with a constant density ratio across the flame and a constant burning velocity, numerical simulations of flame propagation into defined, non-decaying turbulent-like flow reveals a succession of growth rate behaviors. Starting with laminar growth, the flame length then acquires an exponential growth rate when the turbulence distorts the early flame so that an inner flame radius is a small fraction of the largest outer radius. As the flame continues to grow, the difference between the inner radius and the outer radius, referred to as the flame zone thickness L{sub Z}, becomes constant and small compared to the flame size--this yields a constant growth rate, but with magnitude much larger than the initial laminar value. The flame size, using either the average radius or the maximum radius, grows like R {approximately} V{sub C} t, where the flame convection V{sub C} is created by volume expansion distributed throughout the flame zone L{sub Z}. This constant growth rate appears to evolve into a power-law growth rate, R {approximately} t{sup 1+q}, where q > 0, similar to the growth of the flame length, L{sub F} {approximately} t{sup 1+p}, where p > q. which follows its exponential growth period. This accelerated growth rate of flame size can be related to the temporal growth in V{sub C}, which is related to a fractal-like nature of the flame length and a constant flame zone thickness. While there is no direct connection with these synthetic simulations, it is noted that large-scale experiments also exhibit a power-law behavior: R {approximately} t{sup 1.5}

Potential model of a 2D Bunsen flame

The Michelson Sivashinsky equation, which models the non linear dynamics of premixed flames, has been recently extended to describe oblique flames. This approach was extremely successful to describe the behavior on one side of the flame, but some qualitative effects involving the interaction of both sides of the front were left unexplained. We use here a potential flow model, first introduced by Frankel, to study numerically this configuration. Furthermore, this approach allows us to provide a physical explanation of the phenomena occuring in this geometry by means of an electrostatic analogy

Transport properties of dense fluid argon

We calculate using molecular dynamics simulations the transport properties of realistically modeled fluid argon at pressures up to $\simeq 50GPa$ and temperatures up to $3000K$. In this context we provide a critique of some newer theoretical predictions for the diffusion coefficients of liquids and a discussion of the Enskog theory relevance under two different adaptations: modified Enskog theory (MET) and effective diameter Enskog theory. We also analyze a number of experimental data for the thermal conductivity of monoatomic and small diatomic dense fluids.Comment: 8 pages, 6 figure

Diffusion in Stationary Flow from Mesoscopic Non-equilibrium Thermodynamics

We analyze the diffusion of a Brownian particle in a fluid under stationary flow. By using the scheme of non-equilibrium thermodynamics in phase space, we obtain the Fokker-Planck equation which is compared with others derived from kinetic theory and projector operator techniques. That equation exhibits violation of the fluctuation dissipation-theorem. By implementing the hydrodynamic regime described by the first moments of the non-equilibrium distribution, we find relaxation equations for the diffusion current and pressure tensor, allowing us to arrive at a complete description of the system in the inertial and diffusion regimes. The simplicity and generality of the method we propose, makes it applicable to more complex situations, often encountered in problems of soft condensed matter, in which not only one but more degrees of freedom are coupled to a non-equilibrium bath.Comment: 10 pages, accepted in Phys. Rev.

Diffusion in Stationary Flow from Mesoscopic Non-equilibrium Thermodynamics

We analyze the diffusion of a Brownian particle in a fluid under stationary flow. By using the scheme of non-equilibrium thermodynamics in phase space, we obtain the Fokker-Planck equation which is compared with others derived from kinetic theory and projector operator techniques. That equation exhibits violation of the fluctuation dissipation-theorem. By implementing the hydrodynamic regime described by the first moments of the non-equilibrium distribution, we find relaxation equations for the diffusion current and pressure tensor, allowing us to arrive at a complete description of the system in the inertial and diffusion regimes. The simplicity and generality of the method we propose, makes it applicable to more complex situations, often encountered in problems of soft condensed matter, in which not only one but more degrees of freedom are coupled to a non-equilibrium bath.Comment: 10 pages, accepted in Phys. Rev.

The Association of Scalar Dissipation Rate Layers and OH Zones with Strain, Vorticity, and 2-D Dilatation Fields in Turbulent Nonpremixed Jets and Jet Flames

Simultaneous PIV and PLIF methods were used to investigate the relationship between vorticity, principal strain rates, and 2-D dilatation on reaction surfaces in nonpremixed planar jet flames and on 2-D scalar dissipation rate layers and iso-scalar surfaces in nonreacting planar jets. Examination of simultaneous vorticity (w z ) contours and PLIF images in unsteady laminar and turbulent flames suggest that the reaction zone is associated with long correlated regions of high vorticity several times the outer-scale frequency, as well as high values of principal compressive strain (s min ) oriented at 45 to the flow direction and low values of negative 2-D dilatation. Compared to the simultaneous nonreacting flow measurements, the association of high s min and negative 2-D dilatation on isoscalar surfaces is similar to the trends observed in the reaction zones of flames. However, significant differences exist in the relationship of s min direction relative to surface orientation and w z a..